The present invention relates generally to water purification, and more particularly to the use of plant cells in suspension to remove metal atoms and explosives from aqueous solution. This invention is the result of Contract No. W-7405-ENG-36 between the Regents of the University of California and the U.S. Department of Energy.
Barium ion (Ba.sup.2+) has been used extensively in the production of conventional explosives in the explosive formulation Baratol, a 2,4,6-trinitrotoluene-based (TNT-based) castable mixture which consists of 76% (w/w) barium nitrate ground to a specific particle size and 24% TNT. Explosives are routinely machined underwater, resulting in the contamination of the aqueous solution with Ba.sup.2+ and TNT.
Four families of high-temperature superconducting ceramic oxides are currently being investigated. Three of these families contain significant amounts of Ba.sup.2+. The environmental impact of the production of such materials on a large scale will likely include the production of effluent containing high concentrations of barium and other toxic metal ions.
Barium is toxic to humans and to other species and must be removed prior to environmental discharge of effluents from production facilities. Environmental Protection Agency standards presently require the removal of this ion to concentrations below 100 ppm. New guidelines may require that substantially less Ba.sup.2+ can be released. Current methods for barium removal include the conversion of barium nitrate into less soluble barium sulfate which can be precipitated from effluent waters prior to their release. The resulting precipitate is subsequently buried. The overall process is relatively expensive and some barium is still released into the environment.
TNT, oxidation products thereof, and other soluble explosive materials are also found in these effluent waters. Most of these compounds are similarly toxic and must be reduced to environmentally acceptable levels before the water may be released. Current technology requires the step-wise removal of Ba.sup.2+ followed by the removal of these explosive compounds with activated charcoal and incineration of the charcoal. A simpler, more efficient process, and one which also removes other toxic materials from the effluent, is needed for the processing of large amounts of effluent prior to environmental discharge.
Remediation of water-borne plutonium and other actinide elements is a likewise well-known problem for the nuclear power industry and for the nuclear weapons complex. Simple, inexpensive, and efficient removal procedures are actively being sought to enable these industries to comply with increasingly stringent environmental regulations and with public concerns.
Plant cell suspension cultures can be selected for growth in concentrations of certain metal ions which are toxic to many other species. Survival may result from the production of small, metal-binding polypeptides which tightly bind all of the toxic ions entering the cells. See, e.g., P. J. Jackson, C. J. Unkefer, J. A. Watt, and N. J. Robinson, "Poly(.gamma.-glutamylcysteinyl)glycine: Its Role In Cadmium Resistance In Plant Cells," Proc. Natl. Acad. Sci. USA 84, 6619 (1987). Alternatively, tolerance may be associated with the ability to exclude the metal ions from the cells. See, e.g., C. D. Foy, R. L. Chaney, and M. C. White, "The Physiology Of Metal Toxicity In Plants," Annu. Rev. Plant Physiol. 29, 511 (1978). The latter reference describes the uptake of metals by whole plants and suggests a role of whole plants in environmental cleanup and stabilization of contaminated sites, but no parallel action has been observed or predicted for plant cell cultures. Certain plants are already being used to stabilize sites contaminated with toxic trace metal ions (See, e.g., R. R. Gemmel, "Colonization of Industrial Wasteland" (Arnold Publishing Company, London, 1977)).
Fletcher et al. have demonstrated in "Metabolism of 2-chlorobiphenyl by Suspension Cultures of Paul's Scarlet Rose," by J. S. Fletcher, A. W. Groeger, and J. C. McFarlane, Bull. Environ. Contam. Toxicol. 39, 960 (1987) that suspension cultures of Rose remove PCBs from solution and chemically modify them.
Accordingly, it is an object of the present invention to substantially reduce the concentration of chosen metal ions from aqueous solution.
Another object of my invention is to substantially reduce the concentration of TNT in aqueous solution.
Yet another object of the invention is to substantially reduce the concentration of other explosives and explosive oxidation products in aqueous solution.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.